A) Field of the Invention
The present invention relates to an information recording apparatus for recording information in discs such as compact disc-recordable (CD-R) and compact disc-rewritable (CD-RW), and to a program for realizing an information recording method.
B) Description of the Related Art
High speed recording at a linear velocity higher than a standard linear velocity (1×linear velocity) has been used for recording data in discs such as CD-R discs and digital versatile disc-recordable (DVD-R).
In high speed recording at a constant linear velocity (CLV), the number of spindle revolutions per minute (rpm) becomes larger in the inner circumferential area of a disc, for example, 8000 rpm in the inner most circumference at a 16×linear velocity. Because of vibrations and the like generated by high speed revolutions, data cannot be recorded correctly in some cases in the disc innermost circumference area.
In a so-called on-the-fly write operation at high speed from a compact disc-read only memory (CD-ROM) drive to a CD-R drive without forming an image file once in a hard disc or the like, according to one method the CD-ROM. drive is driven at a high constant angular velocity (CAV) to reproduce data and the CD-R drive is driven at a high CLV to write the data. The linear velocity of a CD-ROM drive in CAV reproduction is about 32× on the outer circumference side and about 16×on the inner circumference side. The amount of write data during reproduction on the inner circumference side becomes insufficient and a so-called buffer under-run occurs and the write operation fails.
In order to solve such a problem, a CD-R recording method has been proposed which uses CAV recording when data is recorded in a disc on the inner circumference side and CLV recording is used when data is recorded in the disc on the outer circumference side. For example, CAV recording starts at the revolution number corresponding to the linear velocity of 12×at the innermost circumference position, and after the linear velocity at this revolution number reaches 16×, CLV recording starts at the 16×linear velocity. By switching between the CAV recording and CLV recording in accordance with recording positions such as inner and outer sides of a disc, the maximum number of revolutions can be lowered and recording errors and the like can be suppressed.
Data is recorded in a disc such as CD-R and DVD-R by radiating a laser beam to the disc. It is necessary to set the laser power to an optimum value at a high precision in accordance with various factors such as the type of a disc and a linear velocity. So-called automatic laser power control (ALPC) is therefore performed to detect a laser power supplied to a disc in parallel with a recording process and to feedback control the laser power so as to radiate an optimum laser power from a laser diode.
Some recording apparatuses perform running optimum power control (OPC) during CLV recording to adjust a recording beam to have an optimum record power. The optimum power sequentially obtained during such running OPC is set to a target value in accordance with which a radiation laser power is subjected to ALPC to reduce recording errors.
The linear velocity changes with time during CAV recording so that the target value of a laser beam of ALPC changes with time. Namely, as recording is performed sequentially toward the outer circumference side of a disc, i.e., as the linear velocity becomes faster, a larger laser power is set as the target value to feedback control the laser power to make it have the target value. For example, if the linear velocity changes from 1×to 20×, the laser power is required to be changed from about 3 mW to about 35 mW.
Even with the apparatuses of the type that CAV recording is performed on the disc inner circumference side and CLV recording is performed on the disc outer circumference side, it is necessary to perform ALPC for both the CAV and CLV recording. A servo gain of ALPC in an apparatus using conventional CLV recording is set to about 100 Hz. It has been found that the following phenomenon occurs if ALPC is performed during CAV recording at the same servo gain as that of CLV recording.
Now consider a β value which is a parameter representative of the quality of a reproduction signal reproduced from a disc whose data was recorded while ALPC was performed during CAV recording at the same servo gain as that of CLV recording.
FIG. 5 is a graph showing a change in the β value relative to a scanning position along the radial direction of a disc. As shown in FIG. 5, it has been found that the β value gradually lowers and then increases stepwise.
The stepwise change in the β value shown in FIG. 5 may be ascribed to the resolution of a laser power which the apparatus can adjust and the β value characteristics as described above. The β value is calculated from (a+b)/(a−b) where a is a peak level (+sign) of the waveform of an eight to fourteen modulation (EFM) signal which is a reception signal returned from an optical pickup, and b is a bottom level (−sign). The β value has the characteristics that it becomes large as the recording laser power becomes large and it becomes small as the linear velocity becomes high. Namely, assuming that the laser power does not change, the β value lowers gradually toward the outer circumference side because the linear velocity becomes high. When the laser power is adjusted (raised), the β value increases. If the adjustment resolution of the laser power is fine, the laser power can be adjusted gently so that the β value also changes gently. Since the actual resolution of a laser power is coarse, the β value changes stepwise as shown in FIG. 5. As the β value changes abruptly, the β value becomes outside the range of good recording characteristics. Therefore, many C1 errors are generated and a percentage of recording errors increases.